The present invention concerns a circuit for mixing superimposed video signal and character display signal.
Generally, a video signal processing apparatus such as a video tap recorder, camcorder, etc. employs circuit for superimposing video signals and a character generator (CG) in order to obtain character displaying information. The circuit for superimposing video signals and the CG serve to insert characters and figures of a desired shape on the screen of a video display. In this case, the circuit for superimposing video signals may randomly establish the position and shape of desired character information per frame, while the CG may only establish limited characters and figures predetermined by a microcomputer.
A conventional circuit for superimposing video signals is disclosed in Japanese Laid-Open Patent Publication Sho 62-298278, which disclosed a circuit for superimposing two frames.
Referring to FIG. 1 for illustrating a conventional circuit generating character display information, a composite video signal produced by video signal processing unit 100 is applied to the superimposed video signal generator 200 so that the superimposed video signal corresponding to each frame is stored into a memory thereof. Meanwhile, the composite video signal of the video signal processing circuit 100 is also applied to mixer MIX1. Thereafter, if an interval is reached during which the composite video signal is not applied to the mixer, the memory of the superimposed video signal generator 200 is read by the mixer MIX1 which applies the composite video signal loaded with the superimposed video signal to mixer MIX2. The CG 300 controlled by a microprocessor separates character displaying information into recording and displaying information which is respectively applied to mixers MIX2 and MIX3. Thus if the recording information from the CG 300 is not applied to the mixer MIX2, the mixer MIX2 causes the composite video signal loaded with the superimposed video signal to be transferred to tape recording unit. However, if the recording information from the CG 300 is applied to the mixer MIX2, it is transferred to the tape recording unit. If not applied with the displaying information from the CG 300, the mixer MIX3 causes the output signal of the mixer MIX2 to be applied to video displaying unit. However, if the displaying information from the CG 300 is applied to the mixer MIX3, it is transferred to the video displaying unit. Thus, such a conventional mixing circuit separately processes recording and displaying information output signal of the CG 300, so that the circuit construction is complicated and a plurality of mixers are required, thus increasing the noise.